Air movement system

ABSTRACT

The invention relates to an air movement system comprising a centrifugal fan unit, wherein the centrifugal fan unit comprises a centrifugal fan coupled to a drive unit, a control unit operationally coupled to said drive unit, an inlet piece forming a inlet duct to the centrifugal fan, which inlet duct has an end facing the centrifugal fan, and an outlet duct, wherein the inlet piece is provided with a first pressure tap and a second pressure tap, the second pressure tap being positioned at distance from the end of the inlet duct facing the centrifugal fan, and the control unit is configured to measure a pressure difference between the first and second pressure tap and to control the centrifugal fan in dependence of the measured pressure difference, characterized in that the first pressure tap is positioned at the end of the inlet duct facing the fan, and in that said control unit is adapted to maintain a set airflow rate out of said outlet duct based on said measured pressure difference via controlling of the rotational speed of said centrifugal fan.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to European Patent Application No. 10152302.5 (filed on Feb. 1, 2010), the full contents of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the invention relate to an air movement system, more particular, to a centrifugal fan unit for providing an air flow in the air movement system, more particular to a centrifugal fan unit with backward-curved blades. Embodiments of the invention further pertains to a ventilation system for a building, in particular, a utility building or a residential building, the ventilation system including the centrifugal fan unit.

BACKGROUND OF THE INVENTION

Ventilation systems in many commercial settings are required, either by regulations or by functional specifications, to have a certain minimum flow rates. For example, in commercial buildings, a minimum level of air flow is required to maintain a healthy air quality within the building. Similarly, in other applications, such as clean rooms, a certain level of air flow must be maintained to allow adequate filtration and removal of airborne particulates.

To ensure that the air flow requirements for a particular system are met, it is advantageous to be able to precisely measure the rate of air flow through the system. Systems without precise flow measuring capability are frequently overdesigned to have excess capacity, and are frequently operated at excess levels to ensure compliance with operating specifications. This adds unnecessarily to the expense of both the systems and their operation.

In addition, filters used in some systems can become clogged with particulates, making them more resistant to air flow over time. This increased resistance may cause the air flow of the system to drop below acceptable levels unless it is precisely monitored and steps are taken to compensate for the increased resistance.

Unfortunately, many methods of measuring air flow in a ventilation system can dramatically decrease the efficiency of the system. The efficiency of a ventilation system is a measure of how readily air flows through the system or, conversely, the system's resistance to air flow. Each component of a system through which air flows presents a certain amount of resistance to air flow. This resistance is determined by the size and shape of the component, and by the nature of any obstacles or surfaces over which the air flows. Generally, components that are wider, smoother, straighter and shorter have less resistance to air flow, and therefore provide a more efficient system.

In order to provide an efficient air movement system, many measuring systems were engineered using all sorts of ventilator devices and combining these with various types of pressure measuring devices.

An example of such a system is disclosed in U.S. Pat. No. 5,586,861, which discloses a centrifugal fan unit having two pressure taps at specific locations to measure the static pressure in order to determine pressure difference. An air flow measuring system can detect small changes in the air flow volume rate. A controller monitors the pressure difference across a flared inlet cone, calculates a flow rate based on the characteristics of the cone, and adjusts the fan speed to maintain a desired air flow. To provide an air movement system, the centrifugal fan unit is build into a housing in an uneconomical way. In fact, air flow in axially, leaves the centrifugal fan unit radially to enter a chamber which has an outlet axially and in line with the inlet.

WO2004/072455 discloses a common ventilator with an airflow restriction and having one pressure sensor at the narrowest part of the restriction and a further pressure sensor at a position that is not further defined but to be “to the opposite”.

Many other documents disclose measurements systems for controlling the flow of air produced by a fan. An example of such a document is GB Patent No. 2457534. WO patent Publication No. 2005/036065 shows the same type of ventilator for ventilating an indoor space and having a heat exchanger. Again, setting such a unit to deliver a constant flow independent of its used and external resistance is a problem. In some systems, the motor speed of a fan unit or ventilator is controlled. This, however, does not provide a constant flow of air.

U.S. Pat. No, 5,129,264 discloses in general a centrifugal pump for fluids and having several pressure sensors at different locations in the annular or spiral housing of the centrifugal pump. No reference is made to an air movement system.

In EP Patent No. 2093428 a simple fan assembly is disclosed having a fan assembly and a multitude of pressure sensors at various locations upstream and downstream of the fan assembly. This again does not provide an accurate flow.

GB Patent No. 2451303 discloses a heat exchanging ventilator having a control unit which controls the speed of the ventilator motor unit. Such a unit is well known in the art. The flow rate, however, proved not to be constant enough. In particular when the resistance of the inlet and outlet system varies or the units are used for different duct systems and air treatment systems, it proved difficult to set and maintain a constant flow.

EP Patent No. 2113726 discloses a ventilating arrangement a casing with fan members with impellers inside the housing for creating an air flow and a heat exchanger inside the housing. According to that application, the fan members are designed to be able to obtain a certain flow rate. The application does not explained how a flow rate is set or maintained.

Experiments showed that the flow rate and the control of the flow rate in such air movement systems can be enhanced.

SUMMARY OF THE INVENTION

In accordance with embodiments of the invention, an object is to provide an enhanced air movement system, in which an air flow rate through a centrifugal fan unit is not dependent on the load or resistance of the air movement system before and after the centrifugal fan unit.

In accordance with embodiments of the invention, the object is achieved by an air movement system having at least one of the following features: at least one centrifugal fan unit including a centrifugal fan which in operation has a rotational direction and which has blades that are curved backward with respect to the rotational direction of the centrifugal fan, a drive unit operationally coupled to the centrifugal fan, a control unit operationally coupled to the drive unit, an inlet piece forming an inlet duct which extends coaxially with a rotational axis of the centrifugal fan, to the centrifugal fan unit, the inlet duct having an end facing the centrifugal fan, and an outlet duct which extends tangentially with respect to the centrifugal fan unit.

In accordance with embodiments of the invention, the inlet piece is provided with a first pressure tap and a second pressure tap, the second pressure tap being positioned at an upstream distance from an end of the inlet duct facing the centrifugal fan and opening essentially in a radial direction with respect to the inlet duct.

In accordance with embodiments of the invention, the control unit is configured to measure a pressure difference between the first pressure tap and the second pressure tap and is configured to control the centrifugal fan based upon the measured pressure difference.

In accordance with embodiments of the invention, the first pressure tap is positioned at the end of the inlet duct facing the centrifugal fan at an inlet duct wall and opening in a tangential direction with respect to the centrifugal fan.

In accordance with embodiments of the invention, the control unit adapted to maintain a set airflow rate out of the outlet duct based on the measured pressure difference via controlling of the rotational speed of the centrifugal fan.

The centrifugal fan unit, in particular with blades that are cured backward with respect to the rotational direction of the fan, proved highly efficient in a ventilation system. In order to provide a constant flow, even after passing of time which usually influences the air resistance of the system and the inlet and outlet ducts, the constant flow can be maintained.

Advantageous embodiments and further ways of carrying out the invention may be attained by the measure mentioned in the dependent claims. In particular, the positioning of pressure determining means such as the pressure taps can be important.

The air movement system is in particular useful in buildings like residential buildings and small utility buildings. In these buildings, the air movement system can be part of a ventilation system, air conditioning system, air heating system, air cooling system, air filtering system, or a combination of any one or more of these systems. The air movement system is in particular useful for a flow rate in a range of about 50-800 m³/hr, in particular in a range of about 50-400 m³/hr.

In particular, it was found that the flow rate of the air movement system could be controlled independent of the amount of resistance in the inlet or outlet, and independent if the resistance (e.g., filter, heat exchanger, etc.) was placed before the inlet or before the outlet. In particular, it was found that proper placement of pressure sensors made it possible to economically use a centrifugal pump in an air movement system.

In accordance with embodiments of the invention, the inlet piece can include an inlet piece part made of polymer material, for instance expanded polystyrene (EPS), in an embodiment connecting to the inlet part of the centrifugal fan unit house. The EPS can, for instance, enclose the housing of the centrifugal fan unit and define the inlet piece part.

The centrifugal fan unit has its outlet duct coupled to a further tube or pipe or in use. The outlet may have little additional air resistance. In a centrifugal pump, a centrifugal fan is provided inside an annular housing or spiral housing, sometimes referred to as “snail house.” The outlet of a centrifugal pump is tangential with respect to the fan. The air inlet of a centrifugal pump is axial with respect to the fan. Usually, it is coaxial with the rotational axis of the fan.

The inlet piece forms an inlet duct which can have an inlet duct partly formed from for instance an EPS part. In front of this inlet duct, usually a resistance increasing unit is provided. An example of such a resistance increasing unit is a heat exchanger, but it can also be an air filter, or a heating or cooling unit.

In accordance with embodiments of the invention, an air movement system can include two centrifugal fan units. For instance, the centrifugal fan units are each part of a centrifugal pump. These two units may be operationally coupled to one control unit. Further embodiments are described in the dependent claims and in the drawings.

Embodiments of the invention further pertains to an air movement system that can include at least one of the following features: a centrifugal fan unit that includes a centrifugal fan operationally coupled to a drive unit, a control unit operationally coupled to the drive unit, an inlet piece forming an inlet duct to the centrifugal fan, the inlet duct having an end facing the centrifugal fan, and an outlet duct.

In accordance with embodiments of the invention, the inlet piece is provided with a first pressure tap and a second pressure tap, the first pressure tap being positioned at the end of the inlet duct facing the fan, and the second pressure tap being positioned at a distance from the end of the inlet duct facing the centrifugal fan.

In accordance with embodiments of the invention, the control unit is configured to measure a pressure difference between the first and second pressure tap and to control the centrifugal fan in dependence of the measured pressure difference.

In accordance with embodiments of the invention, the control unit is configured to maintain a set airflow rate out of the outlet duct based on the measured pressure difference via controlling of the rotational speed of the centrifugal fan.

It will be clear that the various aspects mentioned in this patent application may be combined and may each be considered separately for a divisional patent application.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing which illustrate, by way of example, various features of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, properties and advantages of embodiments of the invention will be explained hereinafter based on the following description with reference to the drawings, wherein like reference numerals denote like or comparable parts, and in which:

FIG. 1 illustrates a perspective view of a centrifugal fan unit in accordance with embodiments of the invention.

FIG. 2 illustrates a front view of the centrifugal fan unit of example FIG. 1, in accordance with embodiments of the invention.

FIG. 3 illustrates a top view of example FIG. 1, in accordance with embodiments of the invention.

FIG. 4 illustrates a side view of example FIG. 1, in accordance with embodiments of the invention.

FIG. 5 illustrates the cross section indicated in example FIG. 2, in accordance with embodiments of the invention.

FIG. 6 illustrates an air movement system including centrifugal fan units, in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Example FIG. 1 shows a perspective view of centrifugal pump 1 with a centrifugal fan unit. Example FIGS. 2-4 show several views of the centrifugal pump shown in example FIG. 1. Example FIG. 5 shows a cross section of the centrifugal pump indicated in example FIG. 2.

Centrifugal pump 1 has a spiral or annular casing 2. Spiral casing or house 2 defines part of inlet duct 10. The direction of incoming air is indicated by arrow I. Example FIGS. 3 and 4 also provide views of the air flow direction I of the incoming air. Provided at the smallest cross-section of inlet duct 10 is fan 3. As illustrated in example FIG. 2, when fan 3 is in operation, its rotational direction is clockwise as indicated by arrow R. House 2 further defines outlet 11. The direction of the outgoing air at outlet 11 is indicated by arrow O. Example FIGS. 2 and 4 also provide views of the air flow direction O of the outgoing air. The direction of outgoing air O is perpendicular to the direction of incoming air I. The direction of outgoing air O is also perpendicular to rotational axis A of fan 3. In fact, outgoing air O is tangential with respect to fan 3.

As illustrated in example FIG. 4, driving unit 15 for fan 3 is provided, and may be an electric driving unit. As illustrated in example FIGS. 1 and 5, schematically shown is channel wall 30 of inlet duct 10. Example FIG. 2 further shows that the blades of fan 3 are bent backwards with respect to rotational direction R of fan 3. Thus, the blades are bent away from inlet 6.

The centrifugal fan unit further includes two pressure taps. First pressure tap 5 provides the pressure at the (downstream) end of inlet duct 10 just before fan 3. In accordance with embodiments, pressure tap 5 includes a length of tube which partially runs along inlet duct 10 of house 2. The tube runs radially with respect to fan 3 in radial tube part 12 into inlet duct 10 and as a bend at the position where inlet duct 10 ends, just before fan 3. There, the tube has tangential tube part 13. Tangential tube part 13 is slightly curved and partially follows the inner surface of inlet duct 10. It follows part of the circumferential circle defining the end of inlet duct 10 before fan 3. Usually, tangential tube part 13 is several centimetres long. Opening 6 of tangential tube part 13 is directed in a tangential direction. In particular, in accordance with embodiments, opening 6 has its cross sectional area in one plane with rotational axis A of fan 3. Opening 6 of pressure tap 5 in accordance with embodiments is a distance of about 0-5 mm away from fan 3. Furthermore, it was found that functions without disturbance if opening 6 is in close spatial proximity or as close as possible to inlet duct wall 30. In accordance with embodiments, opening 6 is at a distance of about 0-5 mm from inlet duct wall 30.

Second pressure tap 4 provides the pressure upstream from first pressure tap 5. The position where the pressure is to be used is best indicated in example FIG. 2 in combination with example FIG. 4. Again, a tube enters from radial direction. In use, a further inlet piece or inlet part will be provided which connects to house 2. Thus, second pressure tap 4 will pass through inlet piece wall 30. Thus, the pressure is used from close to the wall of inlet duct wall 30. In fact, experiments showed that good results were obtained with second pressure tap 4 extending about 0-3 mm from inlet piece wall 30. The cross sectional area of opening 8 of tube 4 is tangent to inlet duct wall 30. In accordance with embodiments, the longitudinal axis of second pressure tap 4 intersects rotational axis A of fan 3.

In use, the pressure difference between pressure tap 5 and pressure tap 4 can be about 0.5 Pa-800 Pa. In particular, the pressure difference between first pressure tap 5 and second pressure tap can be about 0.5 Pa-300 Pa. The two pressure taps 4, 5 connect to a control unit. The control unit can include a pressure difference sensor. The pressure difference relates to the flow rate of centrifugal fan unit 1. The control unit will have a set value for the flow rate of centrifugal fan unit 1, and using the pressure difference, the control unit will regulate the flow rate of centrifugal fan unit 1 and keep it constant on the set value. In order to accomplish this, the control unit will set the power of the drive unit of fan 3.

In accordance with embodiments, pressure taps 4, 5 can be positioned essentially axially in line. Pressure taps 4, 5 can be positioned essentially on a line parallel with respect to the rotational axis of fan 3. The line can be close to or in line with inlet duct 10 or inlet duct wall 30. In accordance with embodiments, pressure taps 4, 5 are spaced at a distance of about 2-10 cm from each other.

It was found the system in accordance with embodiments of the invention is particularly suitable for cases where a constant flow rate of air at outlet duct 11 is required, in particular, if the flow rate needs to be in a range of about 50-800 m³/hr. Especially, the system in accordance with embodiments of the invention is designed for a constant flow rate in a range of about 50-400 m³/hr. In the system in accordance with embodiments of the invention, a flow rate can be set, and independent of the ducts this flow rate will be maintained, even after passing of time. In such a flow rate, it was found that pressure taps 4, 5 can have an opening with a diameter of about 1-2 mm and a cross-sectional area of about 0.7-3.5 mm².

As illustrated in example FIG. 6, in accordance with embodiments, an air movement system is shown having the centrifugal fan units illustrated in example FIG. 1. Housing 20 holds two centrifugal fan units 1, 1′. Unit 1 has outlet duct O, unit 1′ has outlet duct O′. Both units 1, 1′ are embedded in EPS units 23, 24. EPS 24 provides part of inlet duct wall 30, usually ducts with a circular cross section, for both units 1, 1′. The air movement system further includes cross flow heat exchanging unit 21 for providing first airflow S1 towards inlet duct wall 30 of centrifugal pump 1′ and second airflow S2 towards inlet duct wall 30′ of centrifugal pump 1 as indicated, and the inflow of air I, I′ is indicated. In fact, the outlets of heat exchanging unit 21 are exits in chambers 32, 32′. These chambers are coupled to inlets 30, 30′ of centrifugal pumps 1, 1′. Heat exchanging unit 21, thus, has an inlet and outlet for first airflow S1 and an inlet and outlet for second airflow S2. Inlet 22 of the air movement system is coupled via duct 31 to the inlet for air flow S2. Inlet 22′ is coupled via duct 31′ to air flow S1. Control unit 25 is coupled to the pressure tubes of both centrifugal pumps 1, 1′ and controls the fan speed, usually though provided power, of both units 1, 1′ to provided a constant, set flow rate.

In accordance with embodiments, alternatively, one centrifugal fan unit 1 can be used in a housing in which unit 1 suspends freely from the outlet duct. The outlet duct is connected to a tube, and the inlet duct draws the air from within the housing which is connected to an inlet tube providing air into the housing.

In the description, the pressure is measured using pressure taps for instance using pressure tubes and a differential pressure sensor. Alternative ways of measuring dynamic and static pressure may be used, measuring the pressure near an inlet duct wall radially in the wall direction at a distance upstream of the fan, and measuring the dynamic pressure near the fan and tangentially in the rotational direction of the fan.

The measures described hereinbefore for embodiments of the invention can obviously be carried out separately or in parallel or in a different combination or if appropriate be supplemented with further measures. It will in this case be desirable for the implementation to depend on the field of application of the centrifugal fan unit. Embodiments of the invention is not limited to the illustrated embodiments. Changes can be made without departing from the idea of the invention. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 

1. An air movement system comprising: at least one centrifugal fan unit including: a centrifugal fan which in operation has a rotational direction and which has blades that are curved backward with respect to said rotational direction of said centrifugal fan, a drive unit operationally coupled to said centrifugal fan, a control unit operationally coupled to said drive unit, an inlet piece defining an inlet duct which extends coaxially with a rotational axis of said centrifugal fan, to the centrifugal fan, said inlet duct having an end facing said centrifugal fan, and an outlet duct which extends tangentially with respect to said centrifugal fan unit, wherein said inlet piece is provided with a first pressure tap and a second pressure tap, said second pressure tap being positioned at an upstream distance from an end of said inlet duct facing said centrifugal fan and opening in a radial direction with respect to said inlet duct, wherein said control unit is configured to measure a pressure difference between said first pressure tap and said second pressure tap and is configured to control said centrifugal fan based upon said measured pressure difference, wherein said first pressure tap is positioned at said end of said inlet duct facing said centrifugal fan at an inlet duct wall and opening in a tangential direction with respect to said centrifugal fan, and wherein said control unit adapted to maintain a set airflow rate out of said outlet duct based on said measured pressure difference via controlling of the rotational speed of said centrifugal fan.
 2. The air movement system of claim 1, wherein said first pressure tap comprises a tube reaching in said inlet piece and which has an opening at the end of the inlet duct facing the fan at a distance of about 0-5 mm from said inlet duct wall.
 3. The air movement system of claim 1, wherein said first pressure tap has an opening spaced at a distance of about 0-5 mm from said inlet duct wall.
 4. The air movement system of claim 3, wherein said opening is provided in the direction of the rotation direction.
 5. The air movement system of claim 1, wherein said first pressure tap has an opening with a cross section which is substantially in a plane through the rotation axis of said centrifugal fan.
 6. The air movement system of claim 1, wherein said inlet duct has a diameter which gradually increases with a distance to said centrifugal fan so as to flares outwardly away from said centrifugal fan.
 7. The air movement system of claim 6, wherein said centrifugal fan unit further comprises an air filter.
 8. An air movement system comprising: a pair of centrifugal fans each having blades that are curved backward with respect to a rotational direction of said centrifugal fans; a drive unit operationally coupled to said centrifugal fans; a control unit operationally coupled to said drive unit; a housing for housing said centrifugal fans, said housing having at least one air inlet including an inlet duct and at least one air outlet having an outlet duct; a heat exchanging unit provided in said housing; a first pressure tap positioned at a downstream end of said inlet duct and configured to provide pressure at a downstream end of said inlet duct; and a second pressure tap positioned at an upstream end of said inlet duct and configured to provide pressure at an upstream end of said inlet duct, said second pressure tap being spaced a predetermined distance from the first pressure tap, wherein said control unit is configured to measure a pressure difference between said first pressure tap and said second pressure tap and is configured to control said centrifugal fans based upon said measured pressure difference.
 9. The air movement system of claim 8, wherein said control unit is adapted to maintain a set airflow rate out of each said outlet duct based on said measured pressure difference via controlling of the rotational speed of each said centrifugal fan.
 10. The air movement system of claim 8, wherein said housing separates air from said at least one air inlet and said at least one air outlet.
 11. The air movement system of claim 9, wherein said housing is adapted to provide two separated air flows which each exchange heat through said heat exchanging unit.
 12. The air movement system of claim 8, wherein the air movement system is part of a system selected from a ventilation system, air conditioning system, air heating system, air cooling system, air filtering system, and any combination thereof
 13. A centrifugal fan comprising: a centrifugal fan having blades which that are curved backward with respect to a rotational direction of said centrifugal fan; a drive unit operationally coupled to said centrifugal fan; a control unit operationally coupled to said drive unit; an inlet duct which extends coaxially with the rotational axis of said centrifugal fan, said inlet duct having an end facing said centrifugal fan; and an outlet duct which extends tangentially with respect to said centrifugal fan, a first pressure tap positioned at a downstream end of said inlet duct in a tangential direction with respect to said centrifugal fan, said first pressure tap configured to provide pressure at a downstream end of said inlet duct; a second pressure tap positioned at an upstream end of said inlet duct and configured to provide pressure at an upstream end of said inlet duct, said second pressure tap being spaced a predetermined distance from the first pressure tap and having an opening at a radial direction with respect to said inlet duct, wherein said control unit is configured to measure a pressure difference between said first pressure tap and said second pressure tap and then control said centrifugal fan based upon said measured pressure difference.
 14. The centrifugal fan of claim 13, wherein said control unit is configured to maintain a set airflow rate out of said outlet duct based on said measured pressure difference via the control of the rotational speed of said centrifugal fan.
 15. The centrifugal fan of claim 13, wherein an opening of the first pressure tap is a distance of about 0-5 mm away from said centrifugal fan.
 16. The centrifugal fan of claim 13, wherein the opening of the first pressure tap is spaced at a distance of about 0-5 mm from an inner wall of said inlet duct wall.
 17. The centrifugal fan of claim 13, wherein said second pressure tap extends a distance of about 0-3 mm from said inlet duct wall.
 18. The centrifugal fan of claim 13, wherein said first pressure tap and said second pressure tap are positioned on a line parallel with respect to the rotational axis of said centrifugal fan.
 19. The centrifugal fan of claim 13, wherein said first pressure tap and said second pressure tap are spaced at a distance of about 2-10 cm from each other.
 20. The centrifugal fan of claim 13, wherein said first pressure tap and said second pressure tap each have an opening with a diameter of about 1-2 mm and a cross-sectional area of about 0.7-3.5 mm². 